Triggered by the CO2 debate, as well as rising energy costs, importance is being increasingly accorded nowadays to a reduced fuel consumption and thus, accordingly, to lower automotive pollutant emissions. Significant technical efforts are underway to design engines and vehicle drives to be more efficient (variable valve stroke, cylinder cutoff, hybrid drives, etc.). These efficiency-enhancing systems make it possible to reduce fuel consumption in the active operating state (which is decisively determinable by engine speed, the engaged gear, velocity and acceleration).
However, the driver selects the active operating state. Various displays in motor-vehicle instrument clusters are used to make the driver aware of a fuel-inefficient operating state. Customary, in this context, are, on the one hand, the fuel-consumption gauge and, on the other hand, what is generally referred to as the “gearshift indicator,” respectively, the “gear indicator.” The purpose of the latter is to indicate to the driver the option of engaging that gear which permits a more energy-efficient driving.
A disadvantage associated with the known, related-art fuel-consumption indicators is that they do not inform the driver to what extent, in the current driving situation, a more power-efficient, respectively more fuel-efficient operating state is possible. Since the displayed numerical values are absolute values, which are only to be interpreted by the driver along the lines of a consumption reduction, such a display does not readily aid the driver in optimizing his/her driving behavior. The fuel-consumption indicator does not provide information as to where, in the current driving situation, a more fuel-efficient operating state resides.
The “shift-up indicators” or the “gear indicators” under the related art are effective aids which facilitate driving in the “correct” gear. However, given a steady-state driving or a driving between two shift points—thus, in the interval from one gear shift to a new gear shift—disadvantages become evident as soon as the need arises to reduce the consumption.
This is clarified on the basis of the steady-state driving example, which is characterized by substantially constant speed: If, by actuating the accelerator, the driver increases the driving torque more than is needed for the steady-state driving, the vehicle will accelerate imperceptibly. However, such low accelerations are not accurately perceivable or distinguishable by the driver in the vehicle. This holds true all the more when the driver is distracted by particular influences or is unfocused. In some instances, the driver does not notice the higher speed until after driving a few kilometers; whereupon he/she removes his/her foot from the accelerator to reduce the driving torque in order to slightly reduce the speed again. In this context, it is particularly disadvantageous when the driver unknowingly accelerates slightly when driving uphill, since the needless acceleration consumes disproportionately more power or fuel. In this case, shift-up indicators are of no further assistance since, with regard to the slight changes, they do not provide any practical recommendation of action to be taken.